The present invention is a surgical device and method. More specifically, it is a surgical device and method which provides an ultrasound transducer assembly mounted on a catheter shaft for ultrasonically coupling to a region of tissue in a body of a patient, and still more specifically for ultrasonically coupling to a circumferential region of tissue at a location where a pulmonary vein extends from an atrium.
The terms xe2x80x9cbody space,xe2x80x9d including derivatives thereof, is herein intended to mean any cavity or lumen within the body which is defined at least in part by a tissue wall. For example, the cardiac chambers, the uterus, the regions of the gastrointestinal tract, and the arterial or venous vessels are all considered illustrative examples of body spaces within the intended meaning.
The term xe2x80x9cbody lumen,xe2x80x9d including derivatives thereof, is herein intended to mean any body space which is circumscribed along a length by a tubular tissue wall and which terminates at each of two ends in at least one opening that communicates externally of the body space. For example, the large and small intestines, the vas deferens, the trachea, and the fallopian tubes are all illustrative examples of lumens within the intended meaning. Blood vessels are also herein considered lumens, including regions of the vascular tree between their branch points. More particularly, the pulmonary veins are lumens within the intended meaning, including the region of the pulmonary veins between the branched portions of their ostia along a left ventricle wall, although the wall tissue defining the ostia typically presents uniquely tapered lumenal shapes.
Many local energy delivery devices and methods have been developed for treating the various abnormal tissue conditions in the body, and particularly for treating abnormal tissue along the body space walls which define the various body spaces in the body. For example, various devices have been disclosed with the primary purpose of treating or recanalizing atherosclerotic vessels with localized energy delivery. Several disclosed devices and methods combine energy delivery assemblies in combination with cardiovascular stent devices in order to locally deliver energy to tissue in order to maintain patency in diseased lumens such as blood vessels. Endometriosis, another abnormal wall tissue condition which is associated with the endometrial cavity of the female and is characterized by dangerously proliferative uterine wall tissue along the surface of the endometrial cavity, has also been treated by local energy delivery devices and methods. Several other devices and methods have also been disclosed which use catheter-based heat sources for the intended purpose of inducing thrombosis and controlling hemorrhaging within certain body lumens such as vessels.
Further, more detailed examples of local energy delivery devices and related procedures such as those of the types just described above are variously disclosed in the following references: U.S. Pat. No. 4,672,962 to Hershenson; U.S. Pat. No. 4,676,258 to InoKuchi et al.; U.S. Pat. No. 4,790,311 to Ruiz; U.S. Pat. No. 4,807,620 to Strul et al.; U.S. Pat. No. 4,998,933 to Eggers et al.; U.S. Pat. No. 5,035,694 to Kasprzyk et al.; U.S. Pat. No. 5,190,540 to Lee; U.S. Pat. No. 5,226,430 to Spears et al.; and U.S. Pat. No. 5,292,321 to Lee; U.S. Pat. No. 5,449,380 to Chin; U.S. Pat. No. 5,505,730 to Edwards; U.S. Pat. No. 5,558,672 to Edwards et al.; and U.S. Pat. No. 5,562,720 to Stern et al.; U.S. Pat. No. 4,449,528 to Auth et al.; U.S. Pat. No. 4,522,205 to Taylor et al.; and U.S. Pat. No. 4,662,368 to Hussein et al.; U.S. Pat. No. 5,078,736 to Behl; and U.S. Pat. No. 5,178,618 to Kandarpa.
Other previously disclosed devices and methods electrically couple fluid to an ablation element during local energy delivery for treatment of abnormal tissues. Some such devices couple the fluid to the ablation element for the primary purpose of controlling the temperature of the element during the energy delivery. Other such devices couple the fluid more directly to the tissue-device interface either as another temperature control mechanism or in certain other known applications as an actual carrier for the localized energy delivery, itself.
More detailed examples of ablation devices which use fluid to assist in electrically coupling electrodes to tissue are disclosed in the following references: U.S. Pat. No. 5,348,554 to Imran et al.; U.S. Pat. No. 5,423,811 to Imran et al.; U.S. Pat. No. 5,505,730 to Edwards; U.S. Pat. No. 5,545,161 to Imran et al.; U.S. Pat. No. 5,558,672 to Edwards et al.; U.S. Pat. No. 5,569,241 to Edwards; U.S. Pat. No. 5,575,788 to Baker et al.; U.S. Pat. No. 5,658,278 to Imran et al.; U.S. Pat. No. 5,688,267 to Panescu et al.; U.S. Pat. No. 5,697,927 to Imran et al.; U.S. Pat. No. 5,722,403 to McGee et al.; U.S. Pat. No. 5,769,846; and PCT Patent Application Publication No. WO 97/32525 to Pomeranz et al.; and PCT Patent Application Publication No. WO 98/02201 to Pomeranz et al.
Cardiac Arrhythmias
Cardiac arrhythmias, and atrial fibrillation in particular, persist as common and dangerous medical ailments and are particularly prevalent among the aging population. A patient with cardiac arrhythmia has abnormal regions of cardiac tissue that do not follow the synchronous beating cycle associated with normally conductive tissue. Instead, the abnormal regions of cardiac tissue conduct aberrant signals to adjacent tissue, thereby disrupting the cardiac cycle and producing an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmia, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self-propagating. In the alternative or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion. Cardiac arrhythmias, including atrial fibrillation, may be generally detected using the global technique of an electrocardiogram (EKG). More sensitive procedures of mapping the specific conduction along the cardiac chambers have also been disclosed, such as, for example, in U.S. Pat. No. 4,641,649 to Walinsky et al. and Published PCT Patent Application No. WO 96/32897 to Desai.
A host of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
Several pharmacological approaches intended to remedy or otherwise treat atrial arrhythmias have been disclosed, such as for example according to the disclosures of the following references: U.S. Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy et al.; and also xe2x80x9cCurrent Management of Arrhythmiasxe2x80x9d (1991) by Hindricks, et al. However, such pharmacological solutions are not generally believed to be entirely effective in many cases, and are even believed in some cases to result in proarrhythmia and long term inefficacy.
Several surgical approaches have also been developed with the intention of treating atrial fibrillation. One particular example is known as the xe2x80x9cmaze procedure,xe2x80x9d as is disclosed by Cox, J L et al. in xe2x80x9cThe surgical treatment of atrial fibrillation. I. Summaryxe2x80x9d Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, J L in xe2x80x9cThe surgical treatment of atrial fibrillation. IV. Surgical Techniquexe2x80x9d, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592 (1991). In general, the xe2x80x9cmazexe2x80x9d procedure is designed to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a prescribed pattern of incisions about the tissue wall. In the early clinical experiences reported, the xe2x80x9cmazexe2x80x9d procedure included surgical incisions in both the right and the left atrial chambers. However, more recent reports predict that the surgical xe2x80x9cmazexe2x80x9d procedure may be substantially efficacious when performed only in the left atrium, such as is disclosed in Sueda et al., xe2x80x9cSimple Left Atrial Procedure for Chronic Atrial Fibrillation Associated With Mitral Valve Diseasexe2x80x9d (1996).
The xe2x80x9cmaze procedurexe2x80x9d as performed in the left atrium generally includes forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the region of the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the arrhythmogenic conduction from the boxed region of the pulmonary veins and to the rest of the atrium by creating conduction blocks within the aberrant electrical conduction pathways. Other variations or modifications of this specific pattern just described have also been disclosed, all sharing the primary purpose of isolating known or suspected regions of arrhythmogenic origin or propagation along the atrial wall.
While the xe2x80x9cmazexe2x80x9d procedure and its variations as reported by Cox and others have met some success in treating patients with atrial arrhythmia, its highly invasive methodology is believed to be prohibitive in most cases. However, these procedures have provided a guiding principle that electrically isolating faulty cardiac tissue may successfully prevent atrial arrhythmia, and particularly atrial fibrillation caused by arrhythmogenic conduction arising from the region of the pulmonary veins.
Less invasive catheter-based approaches to treat atrial fibrillation have been disclosed which implement cardiac tissue ablation for terminating arrhythmogenic conduction in the atria. Examples of such catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers. Some specifically disclosed approaches provide ablation elements that are linear over a defined length and are intended to engage the tissue for creating the linear lesion. Other disclosed approaches provide shaped or steerable guiding sheaths, or sheaths within sheaths, for the intended purpose of directing tip ablation catheters toward the posterior left atrial wall such that sequential ablations along the predetermined path of tissue may create the desired lesion. In addition, various energy delivery modalities have been disclosed for forming atrial wall lesions, and include use of microwave, laser, ultrasound, thermal conduction, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall.
Further more detailed examples of ablation device assemblies and methods for creating lesions along an atrial wall are disclosed in the following U.S. patent references: U.S. Pat. No. 4,898,591 to Jang et al.; U.S. Pat. No. 5,104,393 to Isner et al.; U.S. Pat. No. 5,427,119; U.S. Pat. No. 5,487,385 to Avitall; U.S. Pat. No. 5,545,193 to Fleischman et al.; U.S. Pat. No. 5,549,661 to Kordis et al.; U.S. Pat. No. 5,575,810 to Swanson et al.; U.S. Pat. No. 5,564,440 to Swartz et al.; U.S. Pat. No. 5,575,766 to Swartz et al.; U.S. Pat. No. 5,582,609 to Swanson; U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No. 5,687,723 to Avitall; U.S. Pat. No. 5,702,438 to Avitall.
Other examples of such ablation devices and methods are disclosed in the following Published PCT Patent Applications: WO 93/20767 to Stem et al.; WO 94/21165 to Kordis et al.; WO 96/10961 to Fleischman et al.; WO 96/26675 to Klein et al.; and WO 97/37607 to Schaer.
Additional examples of such ablation devices and methods are disclosed in the following published articles: xe2x80x9cPhysics and Engineering of Transcatheter Tissue Ablationxe2x80x9d, Avitall et al., Journal of American College of Cardiology, Volume 22, No. 3:921-932 (1993); and xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation,xe2x80x9d Haissaguerre, et al., Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996).
In addition to the known assemblies summarized above, additional tissue ablation device assemblies have also been recently developed for the specific purpose of ensuring firm contact and consistent positioning of a linear ablation element along a length of tissue. These assemblies anchor the element at one or more predetermined locations along the length of tissue, such as in order to form a xe2x80x9cmazexe2x80x9d-type lesion pattern in the left atrium. One example assembly includes an anchor at each of two ends of a linear ablation element. The anchors are used to secure the ends to each of two predetermined locations along a left atrial wall, such as at two adjacent pulmonary veins, so that tissue may be ablated along the length of tissue extending therebetween.
In addition to attempting atrial wall segmentation with long linear lesions for treating atrial arrhythmia, other ablation devices and methods have also been disclosed which are intended to use expandable members such as balloons to ablate cardiac tissue. Some such devices have been disclosed primarily for use in ablating tissue wall regions along the cardiac chambers. Other devices and methods have been disclosed for treating abnormal conduction of the left-sided accessory pathways, and in particular associated with xe2x80x9cWolff-Parkinson-Whitexe2x80x9d syndromexe2x80x94various such disclosures use a balloon for ablating from within a region of an associated coronary sinus adjacent to the desired cardiac tissue to ablate. Further more detailed examples of devices and methods such as of the types just described are variously disclosed in the following published references: Fram et al., in xe2x80x9cFeasibility of RF Powered Thermal Balloon Ablation of Atrioventricular Bypass Tracts via the Coronary Sinus: In vivo Canine Studies,xe2x80x9d PACE, Vol. 18, p 1518-1530 (1995); xe2x80x9cLong-term effects of percutaneous laser balloon ablation from the canine coronary sinusxe2x80x9d, Schuger C D et al., Circulation (1992) 86:947-954; and xe2x80x9cPercutaneous laser balloon coagulation of accessory pathwaysxe2x80x9d, McMath L P et al., Diagn Ther Cardiovasc Interven 1991; 1425:165-171.
Cardiac Arrhythmias Originating from Foci in Pulmonary Veins
As discussed above, some modes of atrial fibrillation are focal in nature, caused by the rapid and repetitive firing of an isolated center within cardiac muscle tissue associated with the atrium. Such foci may act as either a trigger of atrial fibrillatory paroxysmal or may even sustain the fibrillation. Various disclosures have suggested that focal atrial arrhythmia often originates from at least one tissue region along one or more of the pulmonary veins of the left atrium, and even more particularly in the superior pulmonary veins.
Less-invasive percutaneous catheter ablation techniques have been disclosed which use end-electrode catheter designs with the intention of ablating and thereby treating focal arrhythmias in the pulmonary veins. These ablation procedures are typically characterized by the incremental application of electrical energy to the tissue to form focal lesions designed to terminate the inappropriate arrhythmogenic conduction.
One example of a focal ablation method intended to treat focal arrhythmia originating from a pulmonary vein is disclosed by Haissaguerre, et al. in xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillationxe2x80x9d in Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre, et al. discloses radiofrequency catheter ablation of drug-refractory paroxysmal atrial fibrillation using linear atrial lesions complemented by focal ablation targeted at arrhythmogenic foci in a screened patient population. The site of the arrhythmogenic foci were generally located just inside the superior pulmonary vein, and the focal ablations were generally performed using a standard 4 mm tip single ablation electrode.
Another focal ablation method of treating atrial arrhythmias is disclosed in Jais et al., xe2x80x9cA focal source of atrial fibrillation treated by discrete radiofrequency ablation,xe2x80x9d Circulation 95:572-576 (1997). Jais et al. discloses treating patients with paroxysmal arrhythmias originating from a focal source by ablating that source. At the site of arrhythmogenic tissue, in both right and left atria, several pulses of a discrete source of radiofrequency energy were applied in order to eliminate the fibrillatory process.
Other assemblies and methods have been disclosed addressing focal sources of arrhythmia in pulmonary veins by ablating circumferential regions of tissue either along the pulmonary vein, at the ostium of the vein along the atrial wall, or encircling the ostium and along the atrial wall. More detailed examples of device assemblies and methods for treating focal arrhythmia as just described are disclosed the following references: U.S. Pat. No. 6,117,101 to Diederich et al.; U.S. Pat. No. 6,024,740 to Lesh et al.; U.S. Pat. No. 6,012,457 to Lesh; U.S. Pat. No. 6,305,378 to Lesh; and U.S. Ser. Nos. 09/642,251 entitled xe2x80x9cDevice and Method for Forming a Circumferential Conduction Block in a Pulmonary Veinxe2x80x9d to Michael D. Lesh. The disclosures of these references are herein incorporated in their entirety by reference thereto.
Another specific device assembly and method which is intended to treat focal atrial fibrillation by ablating a circumferential region of tissue between two seals in order to form a conduction block to isolate an arrhythmogenic focus within a pulmonary vein is disclosed in U.S. Pat. No. 5,938,660 to Swartz et al. and a related Published PCT Patent Application No. WO 99/00064.
In particular, certain tissue ablation device assemblies that incorporate ultrasound energy sources have been observed to be highly efficient and effective for ablating circumferential regions of tissue where pulmonary veins extend from atria. However, the efficiency of ultrasonic output from such a source has been observed to be directly related to the structural coupling of the transducer to the underlying delivery member or catheter shaft. The transducer output is damped whenever it is in contact with any sort of mounting means between the back or inner side of the transducer and the catheter shaft, even according to known modes using elastomeric mounting structures sandwiched between the transducer and the shaft. Several known ultrasound transducer mounting examples provide support structures that extend between the transducer and the underlying support member, such that for example the transducer rests on the support member which rests on the delivery member. Further more detailed examples of such ultrasound transducer support structures are disclosed in the following references: U.S. Pat. No. 5,606,974 to Castellano; and U.S. Pat. No. 5,620,479 to Diederich. Further examples of structural support designs for ultrasound transducers on catheter shafts are disclosed in published PCT Patent Application PCT/US98/09554 (WO98/49957) to Diederich et al.
Further to the previously disclosed ultrasound transducer mounting structures and arrangements, it is desirable for the mounting structure to provide sufficient support and positioning for the transducer. It is also desirable that such a mounting structure provides for air backing between the transducer and the underlying delivery shaft in order to isolate ultrasound transmission radially away from the catheter shaft and toward tissue surrounding the shaft. It has been observed that such air backing helps prevent heat build-up in the region, as the vibrational ultrasound energy has been observed to superheat other materials in contact therewith which absorb the energy (airbacking actually reflects the energy radially outwardly as desired). Therefore, such air backing is particularly desirable for high operational powers associated with therapeutic ultrasound ablation transmission. It is also desirable that such a mounting structure adequately supports the transducer while minimizing the vibrational damping of the transducer during operation. The present invention addresses these desires.
The present invention provides various improved catheter constructions and associated methods of manufacture for mounting an ultrasound transducer onto a catheter shaft while minimizing the damping of the transducer associated with the structural coupling. In several of the construction variations, the transducer is suspended about an inner member (e.g., the catheter body) absent any support structure between the catheter and the transducer along the length of the transducer. That is, transducer mounting is accomplished without the use of internal mounting members and/or elastic member in the space between the inner member and the transducer. Such mounting arrangements support the transducer and are attached to the inner member (or to an assembly of members) at points proximal and distal of the ultrasound transducer.
In one mode of the present invention, an ultrasound ablation apparatus is provided with reduced transducer damping. The apparatus comprises an elongate catheter body having proximal and distal end portions, an outer wall and an outer diameter; a cylindrical ultrasound transducer coaxially disposed over the catheter body, the ultrasound transducer having proximal and distal end portions, an inner wall and an inner diameter which is greater than the outer diameter of the catheter body. Consequently, an air gap is provided in a radial separation between the inner wall of the ultrasound transducer and the catheter body. The apparatus also includes a support structure for suspending the ultrasound transducer in a substantially fixed coaxial position relative to the catheter body. The support structure contacts the outer wall of the catheter body at locations proximal and distal to the proximal and distal end portions of the ultrasound transducer, respectively. Accordingly, the support structure holds the ultrasound transducer without contacting the inner wall of the ultrasound transducer, thereby maintaining the radial separation while reducing transducer damping.
In one preferred mode of the ultrasound ablation apparatus, the ultrasound transducer is shaped to ablate a circumferential region of tissue. The transducer may include at least one transmissive panel.
In another aspect of the ultrasound ablation apparatus, at least a substantial portion of the radial separation is sealed by the support structure to prevent external fluids from entering the radial separation. A gas may be sealed within the radial separation. Alternatively, a liquid maybe sealed within the radial separation.
The ultrasound ablation apparatus of the present invention may include first and second flanges extending axially from the proximal and distal end portions of the ultrasound transducer, respectively, the support structure being coupled to the first and second flanges. The support structure may comprise first and second elastomeric O-rings disposed on the catheter body such that the first and second O-rings engage the first and second flanges. In a variation of this mode, the support structure may comprises first and second sleeves disposed on the catheter body and fitted over the first and second flanges, to secure the ultrasound transducer relative to the catheter body. In another variation, the support structure may comprise first and second splines disposed on the catheter body such that the first and second splines engage the first and second flanges. Alternatively, the support structure may comprise first and second annular members disposed along the catheter body such that the first and second annular members engage the first and second flanges.
In another aspect of the present invention, the support structure may comprise first and second annular members disposed on the catheter body, wherein the first and second annular members frictionally engage the proximal and distal end portions of the ultrasound transducer. The support structure could also comprise a shrink-wrap cover layer disposed around the ultrasound transducer.
In one preferred embodiment, the ultrasound ablation apparatus of the present invention may include an expandable member adapted to engage a circumferential region of tissue. In this mode, the ultrasound transducer is located inside the expandable member and acoustically coupled to the expandable member. The expandable member may be an inflatable balloon.
In a variation to the expandable member embodiment, the ultrasound ablation apparatus may also have a cooling chamber between the ultrasound transducer and the expandable member. The cooling chamber is adapted to allow a cooling fluid to flow over said ultrasound transducer. Further, this mode may include a source of pressurized cooling fluid and a cooling fluid lumen in the catheter body. The lumen may have a distal port opening into the cooling chamber. The ultrasound ablation apparatus may also incorporate a thermocouple for monitoring temperature along at least a portion of the circumferential region of tissue engaged by the expandable member.
The ultrasound ablation apparatus of the present invention may also include at least one electrical lead coupled to the ultrasound transducer.
In a variation of the mounting structure, the apparatus may comprise fillets located proximal and distal to proximal and distal end portions of the ultrasound transducer for sealing the radial separation from entry of external fluids and providing a smooth surface for insertion of said ultrasound ablation apparatus into a body structure.
In another variation, the ultrasound ablation apparatus may include a guidewire lumen extending through at least a portion of the catheter body for slidably engaging a guidewire.
In another variation to the present invention, the appartus may comprise an elongate catheter body; and an cylindrical ultrasound transducer having first and second ends and inner and outer surfaces. The ultrasound transducer is mounted coaxially on the catheter body such that a radial separation is provided between the ultrasound transducer and the catheter body for mechanically isolating the ultrasound transducer from the catheter body. In this mode, the support structure is coupled to the ultrasound transducer and the catheter body to maintain at least a region of the radial separation for reducing acoustic damping caused by the support structure.
In variations to this mode, annular end members may be provided with a metallic exterior surface adapted to engage the inner surface of the ablation element. This mounting mode may also include an annular intermediate portion, located between the first and second annular members and the catheter body.
In another variation, the support structure may comprise a substantially tubular member disposed over the catheter body. The tubular member has proximal and distal end regions and an intermediate region. The proximal and distal end regions are formed with a larger diameter than the intermediate region. The ultrasound transducer is disposed over the intermediate region such that it is axially contained by the proximal and distal end regions.
In another variation, the support structure may comprise at least one mandrel extending axially along the catheter body The at least one mandrel engages the catheter body and the inner surface of the ultrasound ablation element. The at least one mandrel may be a polyimide tube. More preferably, the at least one mandrel comprises a plurality of polyimide tubes positioned substantially uniformly around the catheter body within the radial separation.
In another variation, the support structure may comprise a braided metal tubular member disposed around the catheter body such that the radial separation is maintained therebetween. The ultrasound transducer is mounted coaxially over the braided tubular member. Alternatively, the support structure may include two braided metal tubular members disposed around the catheter body with an axial gap therebetween. The ultrasound transducer may be mounted to the braided tubular members thereby bridging the axial gap.
In another aspect of the invention, the support structure may comprise two truncated conical members, each having a first end with a large diameter and a second end with a small diameter. The conical members are disposed over the catheter body such that the first ends face inward and the second ends face outward. The inner surface of the ultrasound transducer is engaged by the first ends of the conical members.
In accordance with another mode of the invention, the support structure may comprise an expandable member disposed over the catheter body and having an outer surface. The inner surface of the ultrasound transducer may then be coaxially engaged by the outer surface of the expandable member.
The modes of the invention are generally adapted to capture air, or another gas as would be apparent to one of ordinary skill, within the mounting structures in order to xe2x80x9cair backxe2x80x9d the transducer. That is, these modes of suspension maintain an air gap between the transducer and the catheter shaft in order to maximize radially outward propagation of the ultrasound waves, as introduced above. In addition, the air space desirably is sealed to prevent fluid infiltration, be it blood or another fluid.
According to further beneficial modes, the ultrasound transducer apparatus and method modes just summarized are applied in a circumferential ablation device assembly which is adapted to couple to and ablate a circumferential region of tissue at a location where a pulmonary vein extends from an atrium. Moreover, the modes described for use with a circumferential ultrasound transducer may also be adapted for use with non-circumferential types of transducers, such as incorporating panel transducers that also benefit by being air backed without mounting members physically located and extending between such transducers and an underlying catheter shaft.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above and are described below. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular mode of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. In addition, further aspects, advantages and features of the invention will become apparent from the following descriptions of the preferred modes of incorporating an ultrasound transducer onto a delivery element.